Why did my shopper get a 'sold out' message at checkout after she got invoiced?
Your shopper comments for an item, successfully gets an invoice, and then gets a 'sold out' message when she goes to check out. Frustrating!
This happens because someone decided to go to your Shopify store directly, and buy the item from there instead of the live sale. In this case, they completely bypassed the commenting system. And so she is effectively 'stealing' an item that someone already claimed with a comment.
If you have this issue, it's recommended to prevent the items that are being sold on your live from being searchable/findable on your website. Or disable your website completely during your live by password-protecting it. Please see this article on how to do that